1. Field of the Invention
This invention relates to the production of crimpable chemical yarns and more specifically to the production of such yarns simultaneously with the generation of potentially crimpable chemical yarns by shaping and heating thereof.
The present invention relates to both the process for the production of such yarns and to the apparatus for carrying out the process.
2. Description of the Prior Art
In the remainder of the description, the term "chemical yarn" denotes any yarn based on an organic material, which is obtained by spinning such material through a spinneret pierced with holes.
As materials suitable for the manufacture of chemical yarns, there may be mentioned, among converted natural polymers, those known under the names cupro, viscose, modal, deacetylated acetate, acetate, triacetate and the like, and among synthetic polymers, those known under the names acrylic, modacrylic, polyamide, polycarbamide, polyester, polyethylene, polypropylene, polyvinyl and the like.
It is well known that, after extrusion, chemical yarns are generally subjected to various treatments intended to impart particular properties, and especially characteristics of bulk and/or of elasticity, to the yarns. In general, the bulk and/or the elasticity is obtained by giving the filaments a suitable permanent crimp or waviness.
One of the most widespread treatments, especially as regards yarns based on a thermoplastic, is the so-called texturizing or crimping treatment, which consists in permanently deforming the yarn. This may be accomplished, for example, by imparting a false twist thereto, compressing it, subjecting it to the action of a jet of fluid, passing it over a sharp edge between gearwheels, and so on, the deformation thus imparted to the filaments being set-in by heat treatment and cooling. This texturizing or crimping operation is generally carried out in a separate stage after spinning.
In order to reduce the cost and increase productivity, it has been proposed to combine the texturizing or crimping operation with a spinning operation. However, although this technique gives good results, it requires the use of hardware in addition to the spinning installation, in order to impart the desired effect to the yarns. For a long time, the producers of chemical yarns have therefore been attempting to obtain yarns or fibers which are crimped directly during the spinning operation, without employing the convention texturizing or crimping processes.
Among the solutions proposed, the best known consists in spinning yarns which are said to have "potential crimp", that is, yarns of which the constitution is such that a crimp or waviness can be developed subsequently by simple drawing and/or heating. Yarns of this type, which are frequently denoted by the expression "bi-component yarns", are obtained, for example by extruding, for each filament forming the yarn, two polymers of different types or the same polymer in two different physical states, the polymers being arranged either side-by-side or in a core-sheath relationship or in a random distribution.
After subsequent treatment, this technique makes it possible to obtain strongly crimped and/or waved yarns, but the technique disadvantageously requires distributing devices in front of the spinneret which are complex, fragile and difficult to produce. Thus, this technique has not been developed.
It has also been proposed to manufacture yarns, having potential crimp, from a single polymer which is spun using conventional spinnerets, the extruded yarn being subjected after extrusion, to an asymmetric heating or cooling process, which theoretically produces a yarn having potential crimp.
It must be recognized that this solution has not given good results, which is easily explained by the fact that the extruded yarn is composed of a plurality of filaments and as a result, it is not possible to modify the structure of each filament in an identical manner. Furthermore, this type of process is rather difficult to carry out.
Finally, it has also been proposed to produce potentially crimpable chemical yarns by creating during spinning, a variation in the viscosity of the polymer mass before passage through the spinneret, so as to obtain in each filament forming the yarn, a viscosity which varies from one side to the opposite side of the same filament, the crimp also being developed by subsequent heat treatment, which treatment is optionally combined with the drawing operation. This type of process is described in French Pat. No. 2,143,793.
In general, according to this document, the material is subjected to asymmetric heat treatment, while it is being extruded, by means of heating elements which act directly on the material inside the spinning holes. This process is also complex and difficult to carry out.
Therefore, it is a feature of the present invention to produce by an improved process potentially crimpable chemical yarn while simultaneously subjecting it to shaping and heat treatment, thereby also achieving actual crimpable yarn.
It is another feature of the present invention to provide an improved process of and apparatus for producing crimpable chemical yarn by drawing and extruding potentially crimpable chemical yarn through an orifice having two generatrices of its peripheral surface while simultaneously subjecting it to assymetricaly heating.